Kenwood TK-2170 Service Manual

Also see for TK-2170 SERIES: Service manual Function reference Instruction manual Instruction manual Specifications

TK-2170242-5. Audio Amplifier CircuitThe demodulated signal from IC701 is amplified by IC10,and goes to AF amplifier through IC13.The signal then goes through an volume control (IC16),and is routed to an audio power amplifier (IC18) where it isamplified and output to the speaker.2-6. Squelch CircuitPart of the AF signal from the IC enters the FM IC (IC701)again, and the noise component is amplified and rectified by afilter and an amplifier to produce a DC voltage correspondingto the noise level.The DC signal from the FM IC goes to the analog port ofthe microprocessor (IC7). IC7 determines whether to outputsounds from the speaker by checking whether the input volt-age is higher or lower than the preset value.To output sounds from the speaker, IC7 sends a high sig-nal to the AM2 line and IC5 sends a high signal to the AM1line, and turns IC18 on through Q23, Q24, Q27, Q28 andQ35. (See Figure 4)3. Transmitter System3-1. Microphone AmplifierThe signal from microphone amplified by IC13 (1/2) andlimited by AGC circuit composed of D30, D31, Q25 and Q26,and goes through mute switch (Q30). IC13 is composed ofhigh-pass filter, low-pass filter and pre-emphasis/IDC circuit.The signal enters the summing amplifier consisting ofIC12 (2/2), and passes through the D/A converter (IC16) forthe maximum deviation adjustment, and is mixed with thelow speed data from the CPU (IC7).The output signal from the D/A converter goes to the VCOmodulation input. The other output signal from the D/A con-verter passes through the D/A converter (IC16) again for theBAL adjustment, and the buffer amplifier (IC17), and goes tothe TCXO modulation input.SPQ22SWIC16VOLIC18AF PAQ23,24,27SWSWQ28,35IC5Shift register2-toneIC15BPF & CompalaterCLK, DATA,STD, LOADNIC10IF AMPIC11LPFIC13AQUA-LIC701FM IFSIGNALDTMFANSQLIC7CPULSDI QT/DQTHSDIAM2AM1Fig. 4 Audio amplifier and squelch circuitMIC Q30IC13(1/2)AMPIC12(2/2)SUMAMPIC17 X701BUFFAMP TCXOVCOAGCSW AQUA-LIC13IC16D30,31Q25,26D/A O2I2IC16D/A O8I8LSDOUTMMUTEFig. 5 Microphone amplifier3-2. Drive and Final AmplifierThe signal from the T/R switch (D518 is on) is amplified bythe drive amplifier (Q603) to 50mW.The output of the drive amplifier is amplified by the RFfinal amplifier (Q604) to 5.0W (1W when the power is low).The RF final amplifier consists of two MOS FET stages.The output of the RF final amplifier is then passed throughthe harmonic filter (LPF) and antenna switch (D604 and D605)and applied to the antenna terminal.3-3. APC CircuitThe APC circuit always monitors the current flowingthrough the RF power amplifier (Q604) and keeps a constantcurrent. The voltage drop at R621, R623 and R629 is causedby the current flowing through the RF final amplifier and thisvoltage is applied to the differential amplifier IC601(1/2).IC601(2/2) compares the output voltage of IC601(1/2) withthe reference voltage from IC7. The output of IC601(2/2)controls the VG of the RF power amplifier, drive amplifier andpre-drive amplifier to make both voltages the same.The change of power high/low is carried out by the changeof the reference voltage.FromT/R SW(D518)Pre-DRIVEAMPDRIVEAMPQ602 Q603RF FINALAMPQ604ANTSW LPFD604,605ANTVDD VGIC601(1/2)IC601(2/2)R621R623R629+BPC(IC7)Fig. 6 Drive and final amplifier and APC circuitCIRCUIT DESCRIPTION